HYPERICINEÆ.
St. John’s Wort (Hypericum perforatum L.). There appears to be no record of poisoning of live stock by this plant in Britain, but Cornevin records that it injured breeding mares fed on lucerne containing it in large proportion. Drying in converting into hay did not render it innocuous. It is only poisonous if eaten in considerable quantity, and in general animals are not likely to eat much of it voluntarily, owing to its resinous odour when crushed, and a bitter and slightly saline taste.
Toxic Principle. The poisonous properties of St. John’s Wort have not been fully investigated, but it is stated to contain an oil and an acrid bitter resin. Ewart says that it “contains an oil whose medicinal value was formerly highly esteemed; but this oil, and the woody nature of the plant, render it somewhat injurious in fodder.” Summers says (Journ. Agric. S. Australia, Sept. 1911, p. 144) that “it is reported to be decidedly injurious, causing horses who eat it to break out in sores, while milk cows have a tendency to dry off owing to its effect on the system.”
Symptoms. In mares, dullness, sinking of head, loss of appetite, slackening of pulse and respiration, dilatation of pupils, defective sight, and lips purple (Müller).
GERANIACEÆ.
Wood Sorrel (Oxalis Acetosella L.). Though rarely likely to be eaten by stock this plant must be mentioned here, as it is considered dangerous on account of its high content of oxalates, which may cause serious illness and diarrhœa, and in the case of sheep even be fatal. Pott says that the milk of cows eating it is with difficulty converted into butter.